In recent years, portable electronic devices have become widely used such as a digital camera and a mobile phone having a camera (imaging device) function that allows the photographing mode (e.g., normal, macro) to be selectively changed (refer to patent literature 1 for instance).
A portable electronic device of patent literature 1 includes a lens advancing device for selectively changing the photographing mode (e.g., normal, macro).
The lens advancing device includes an advancing ring holding the lens unit, a holder supporting the advancing ring rotatably around the optical axis of the lens unit, a cover holding the advancing ring onto the holder, and an operation unit for rotating the advancing ring.
The lens advancing device is provided with what is called a cam mechanism for transforming rotary motion of the advancing ring to reciprocating motion (back-and-forth motion along the optical axis) of the lens unit. Concretely, the lens advancing device has a cam surface formed on one of the advancing ring and holder, and an abutting part formed on the other of the advancing ring and holder and is engageable with a cam surface. When the operation unit rotates the advancing ring, the engaging position of the abutting part with a cam surface is changed and thereby the advancing ring is displaced along an optical axis of the lens unit. Consequently, the lens unit is displaced along the optical axis.
The lens advancing device is provided on its advancing ring with an elastic body made of synthetic rubber material that is elastically deformable. The lens advancing device is structured so as to exert an elastic force of the elastic body interposed between the advancing ring and the cover in a compressed state, on the advancing ring to press the abutting part against a cam surface.
That is to say, the lens advancing device structured as above uses an elastic force (urging force) caused by compress-deformation of the elastic body for urging the advancing ring. Accordingly, to obtain a sufficient urging force (the amount of compress-deformation) of the elastic body, the hardness of the material of the elastic body itself needs to be set low.
However, a lower hardness of the elastic body itself results in an insufficient urging force on the advancing ring. On the other hand, a higher hardness of the elastic body itself results in an insufficient urging force (the amount of compress-deformation) of the elastic body. Consequently, an error in shape dimensions, for instance, of the elastic body undesirably causes an urging force on the advancing ring to largely fluctuate.
Further, a large fluctuation of an urging force by the elastic body on the advancing ring when switching between photographing modes (e.g., normal, macro) causes resistance in rotational operation of the advancing ring by the operation unit to largely change. Consequently, the user feels uncomfortable when rotating the advancing ring.